This proposal to purchase a modern infrared interferometer, Digilab Model FTS-20E/D, will facilitate borader application of vibrational spectroscopy to biomedical problems and assure a state-of-the-art capability for infrared biospectroscopy. The users propose to apply this technology to problems of structure and biological control in cytochrome c oxidase, and related metal proteins, conformational states of 5SRNA, enzyme structures involved in mercury detoxification, and questions of membrane fluidity. This system, with accessories, will permit a wide range of sampling conditions between 10 cm-1 and 10,000 cm-1 at temperatures between 1.8K and 300K in the dark and in the presence of photolyzing radiation. The laboratory is organized to permit dedicated instrumental use with special sampling conditions for sufficient periods of time to conduct experiments with single molecular vibrations in complex biological systems.